This research was a detailed study of ryegrass (Lolium perenne L.) and the susceptibility to the Drechslera siccans pathogen. It was important to determine whether rapid analytical techniques, applied to the biochemical analysis of L. perenne, could identify and facilitate the removal of susceptible germplasm from the breeding programme. The remaining resistant plants were then positively selected for and used within the further breeding of new cultivars. The study focused upon the standardisation of tire-disease scoring value (OSV) for the O. siccans assessment, and examined the application of near infrared reflectance spectroscopy (NIRS), digital image analysis(DIA), thermogravimetric analysis (TGA) and fourier transformed infrared microscopy (FTIRm). The research aimed to enhance the breeding of new cultivars with greater resistance to D. siccans. Traditional breeding techniques of L. perenne cultivars requires selection and trial examination over many years. This research evaluated germplasm in F2 clonal row trials, which were designed to determine the effect of D. siccans infection. The trial design facilitated the application of rapid assessment techniques in the selection process. Phenotyplc examination of F2 plants resulted in the discovery of a series of differential plants, which had a high level of consistent scoring for DSV, NIRS and DIA, plus using a unique algorithm created the disease assessment tool (OAT). Using OAT a distinct strategy was developed to select L. perenne germplasm, which had consistently high levels of resistance to O. siccans. The TGA and FTIRm research explored the association of macromolecule structure with disease analysis. The TGA result showed a strong positive correlation with WSC analysis of L. perenne (R=0.968) but was unable to determine whether high WSC grass experienced higher susceptibility to D. siccans. Spectrometric analysis of necrotic lesions (caused by O. siccans) using FTIRm identified unique spectra for susceptible L. perenne material. This unique biochemical fingerprint analysis has the potential of quickly identifying susceptible L. perenne with the deselection of F2 plants. This study investigated the selection process of L. perenne germ plasm within a breeding programme, but also included a high level of spectrometric (especially NIRS) and DIA assessment. The assessment strategy developed new L. perenne cultivars these showed a positive outcome for breeding highly productive and more D. siccans resistant L. perenne cultivars. A detailed knowledge was gained for L. perenne phenotypic characteristics and' of the structural biochemistry of the L. perenne. Hence, the product of this research will potentially increase grassland production on farms

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This thesis uses a published model of phoma stem canker of oilseed rape as a case study to investigate some aspects of unreliability in disease prediction models and their application to predict climate change effects on disease. The published model had four stages, predicting the threshold date for fungicide spray (10% of plants with phoma leaf spots), the onset of stem canker symptoms, the final disease severity pre-harvest and yield loss. For each stage the regression model was linear. In order to accurately represent disease progress, linear disease models require a linear relationship between fungal development and the predictive variables used. Response to temperature was investigated in vitro and in plonto for the two pathogens involved in phoma stem canker. In vitro the radial growth rate was linear across the range of temperatures commonly experienced by crops in the UK. In planta, however, the reaction norm for canker severity caused by the more aggressive pathogen, L. maculans, suggested that it had a lower temperature optimum close to the present highest daily mean temperatures in the UK. In planta results for the less aggressive L. biglobosa were inconclusive. Internal basal stem temperatures were monitored in oilseed rape crops. The temperature experienced by the fungus during canker development at the base of the stem is buffered from the extremes of air temperature and is dependent on plant growth stage. An exploration of predictions versus observed disease data for recent years was made. This revealed the model's inability, in its present form, to make accurate predictions in years with unusual rain patterns during summer and autumn and in the presence of modern resistant cultivars. The implications for model accuracy of predicting disease in future climates for the UK in the 2020s, 2050s and 2080s are discussed.

Aphids cause considerable harm to a variety of crops each year due to damage from feeding and the transmission of viruses. Effective, conventional pesticides that are authorised for use are in continuous decline; simultaneously many of the current biological pesticides fail to meet required efficiency. Increasing demands for improved food security mean that a solution for this problem is needed. Plant surfaces are well known to provide a niche for many bacteria. Some species of bacteria possess pathogenic qualities and are known to kill or incapacitate insects. Therefore there is the potential for the discovery of a direct bacterial application, or the opportunity to manipulate the crop environment in order to encourage the colonisation of these beneficial bacteria. In this project we aim to identify bacteria from plants and screen them for toxicity against aphids and their relatives. Investigations will be carried out into their host specificity, methods of pathogenicity, and potential application methods, with the hope of identifying suitable bacteria for use as a pesticide.

Plant parasitic nematodes (PPNs) undermine agriculture globally, through direct parasitism of crops and/or as vectors of secondary infections. The impacts are so severe and far reaching that quantifying the associated damage is virtually impossible. With the growing pressures on modern agriculture to increase productivity and to meet consumer demands, while facing limitations from increased biotic and abiotic challenge (despite slowing improvements in the development of new varietal germplasm), there is a widening gap between high yielding, high quality stock, and demand requirements. This study investigated the PPN populations in Northern Ireland agricultural land to enable identification of potential threats to plant-based agriculture systems from economically damaging species. Here, the extent of PPN diversity in Northern Irish agriculture was illustrated, with the identification of 18 different genera and the presence of statistically significant trends linking specific nematode presence and abundance with environmental and edaphic factors. Most notably, was the apparent significant increase in root knot nematode (Meloidogyne spp.) populations that were present at significantly higher incidences than those reported in the historical records. The detection of Meloidogyne minor in agricultural fields further strengthened the belief that this recently described species is in fact endemic to the British Isles. Potential nematode control management strategies were investigated and Northern Irish recommended cereal and pasture varieties were screened for the presence of naturally occurring resistance. The direct effects of several plant derived compounds and biostimulants on PPNs were investigated. Many of the compounds screened displayed attractive or repellent properties, while further analysis of ET and SA suggested Meloidogyne incognita juveniles possess memory and associative learning traits. In addition, the effects of biostimulant pre-treatment on crop plant health and resistance to nematode challenge was examined. Molecular-level impacts on the main plant defence signalling hormones (salicylate, jasmonate and ethylene) of biostimulant pre-treatment and! or 'priming' of plants during nematode challenge was assessed. Key defence related marker genes were compared at early stage infection time points (3 and 7 days post inoculation) in biostimulant pre-treated Arabidopsis thaliana.

Populations of pathogenic and non-pathogenic bacteria were studied in Phaseolus vulgaris. Virulent isolates of the homologous pathogen Pseudomonas phaseolicola multiplied at rates and to final populations which suggested that no inhibitory reaction with the plant was involved. Necrosis-inducing heterologous pathogens multiplied at lower rates and to lower final populations than the homologue. Non-pathogens were static in tissue. A suggestion made elsewhere that the behaviour of non-pathogens and pathogens was determined by their different oxidase activities was not supported. The growth of non-pathogenic bacteria co-inoculated into bean leaves with the homologous or heterologous pathogens was stimulated, indicating that the plant intercellular environment was modified by pathogens to favour general bacterial growth. Inoculation of non-pathogens with nutrient amendments did not affect their behaviour in plant tissue, but when leaves were held in water-soaked conditions following inoculation, non-pathogens multiplied and the heterologous pathogens were stimulated to the same rate and almost to the same final population of the homologue. Free water appears to be the initial limiting factor for the multiplication of bacteria in the intercellular spaces. The growth of heterologous pathogens co-inoculated with the homologue was also stimulated. Pathogenic specificity may be explained by the action of bacterial toxins acting directly or indirectly to increase host cell membrane permeability. When beans were challenged with high concentrations of inocula of non-pathogens, a general inhibition occurred against pathogenic bacteria which were subsequently inoculated. Inhibition induced in plants by bacteria may regulate their final populations.

The work contained in this thesis investigates competition for nutrients between epiphytic micro-organisms and Botrytis cinerea or conidia of other plant pathogens. The hypothesis that epiphytic bacteria inhibit germination of nutrient-independent conidia by acting as a nutrient sink and competitively deplete the endogenous reserves of the conidia during the germination period, was tested. Both the uptake of 14C-label, originally derived from conidia, and the loss of label from conidia on a model leaching system were followed and compared. It was found that conidia were most susceptible to loss of endogenous reserves early during the germination period (up to 5h). A relatively small loss of endogenous reserves, either to bacteria or in the leaching system, was associated with inhibition of germination. However, carbon dioxide evolution from conidia was decreased in the presence of bacteria, whereas leaching did not cause such a decrease when compared with controls. Tests failed to demonstrate the presence of any compounds produced by bacteria which inhibited the germination of conidia. From these studies it appeared likely that selective competition for particular essential nutrients was limiting the germination of -conidia. This was further investigated in vitro , it being shown that amino acids, at levels which were normal on the leaf surface, stimulated germination, whereas glucose, fructose and sucrose had little effect. When amino acids were present with glucose (again at levels normal on the leaf surface) , the uptake of amino acids by bacteria after 5h was Correlated with inhibition of germination of conidia. This relationship held .for a number of different epiphytic micro-organisms, including yeasts. No such correlation was apparent between inhibition of germination and uptake of amino acids, when this was the sole added nutrient. Similar studies were then carried out on the leaf surface. The leaf itself did not reabsorb a significant quantity of nutrients lost to its surface and a relatively large quantity of soluble carbon compounds was detected in drops, as soon as these were placed on dry leaves. The relationship between amino acid uptake by epiphytic microbes and inhibition of germination obtained from studies, using a tracer quantity of 14C-amino acids, was almost identical to that observed in the in vitro studies. On the leaf, approximately ten times fewer micro-organisms were required to deplete the amino acid levels and. bring about inhibition. Leaves, which had been wetted 24h previously, supported sufficient numbers of epiphytes to deplete the tracer amino acids and inhibit the germination of conidia. When three other plant pathogens were tested, two (Phoma betae 8c Cladosporium herbarum) behaved similarly to B. cinerea. However, the germination of Colletotriehum dematium _f spinaciae conidia was not inhibited and in in vitro tests appressoria were formed more rapidly from conidia in the presence of bacteria than from control conidia.

The diet, habitat preferences, and foraging behaviour of stoats and living in an area of farmland near Newburgh, Aberdeenshire were studied over a period of years. Additional information was collected from nearby areas of sand dune and mixed farmland and woodland. The differences in size between the species, and sexual dimorphism were assessed by measuring nine body parameters of 54 stoats and 87 weasels. Trophic niche overlap was assessed quantitatively from an analysis of 301 scat and gut samples. The diets of both sexes of both species were very similar though larger predators tended to take larger prey items more often. Radio-tracking techniques were applied to both species during the last two years of the study, over 1300 hours of field observations being made. Both species hunted in the same areas and no differences in habitat preferences were noted. Niche overlap in habitat utilization was assessed quantitatively for ten farmland vegetation-type classifications. Male weasels were territorial. Territoriality in male stoats was not established. Female stoats had contiguous exclusive home ranges but no territorial defense was observed. Female weasels had non-contiguous home ranges. The home ranges of different sexes and different species overlapped. Home range area was much larger than other published estimates but the area within the minimum convex polygon boundaries that was exploited by the animals was similar to estimates from areas of homogeneous habitat. The abundance and distribution of small mammals were monitored in known steat and weasel hunting areas. Breeding of small rodents ceased between November and March/ April and numbers were very low in some habitats by March. It was concluded that exploitation competition between stoats and weasels for small rodents in spring was very probable but that differences in access to small rodents and the presence of some alternative prey at times of small rodent shortage enabled both species to coexists The possibility of interference interactions occurring was established but thought to be unimportant in maintaining the coexistence of the two species on farmland.